FILM THICKNESS MEASURING METHOD AND FILM THICKNESS MEASURING DEVICE

PROBLEM TO BE SOLVED: To shorten the measurement time without necessitating accurate alignment for a position suitable for film thickness measurement. SOLUTION: A plurality of sampling lines n1 to n5 which obtain a profile of a light receive signal of a picture image cross section are set to judge a picture image having the best image formation condition in a two-dimensional picture image received by a CCD light receive element. Respective light receive signal differences are obtained per adjacent image address i, j from these image cross section profile information to adopt the image in which an average value of these differences becomes the maximum as a position detection screen in a position detection image processing part. A position (xp, yp) in the two-dimensional picture image is obtained by the position detection picture image processing part using a specific pattern or mark for position detection registered in advance as standard from within the adopted screen. A position (xm, ym) or region S suitable for film thickness measurement is put in coordinates and determined using this position (xp, yp) as standard by image processing of a film thickness measurement suitable position selection part 55 to measure a film thickness for this suitable position.